Improve error handling in background workers

What does this MR do and why?

Recently we were getting the errors related to the incorrect error handling. Example:

1. ActiveRecord::QueryCanceled is raised when searching for an object by id logs (internal).
2. The error is caught by the rescue block and handled by process_package_file_error.
3. package_file doesn't exist => different error is raised undefined method 'project_id' for nil:NilClass (NoMethodError) sentry (internal).

This MR adds the guard to the rescue block to verify if package file exists before processing the error.

References

• logs (internal)
• sentry (internal)

Screenshots or screen recordings

No.

How to set up and validate locally

The changes are straightforward and, I think, covering them with the tests should be enough.

MR acceptance checklist

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Related to #578214